EntityCollection<TEntity>.Remove(TEntity) Method

Reference

Definition

Namespace:: System.Data.Objects.DataClasses

Assembly:: System.Data.Entity.dll

Important

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Removes an object from the collection and marks the relationship for deletion.

public:
 virtual bool Remove(TEntity entity);

public bool Remove (TEntity entity);

override this.Remove : 'Entity -> bool

Public Function Remove (entity As TEntity) As Boolean

Parameters

entity: TEntity

The object to remove from the collection.

Returns

Boolean

true if item was successfully removed; otherwise, false.

Implements

Remove(T)

Exceptions

ArgumentNullException

entity object is null.

InvalidOperationException

The entity object is not attached to the same object context.

-or-

The entity object does not have a valid relationship manager.

Examples

This example is based on the Adventure Works Sales Model. To run the code in this example, you must have already added the AdventureWorks Sales Model to your project and configured your project to use the Entity Framework. To do this, complete the procedures in How to: Manually Configure an Entity Framework Project and How to: Manually Define the Model and Mapping Files.

This example uses the Remove method to remove one of the entities from the collection and then calls the Contains method to determine whether the object was removed from the collection.

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    Contact contact = new Contact();

    // Create a new SalesOrderHeader.
    SalesOrderHeader newSalesOrder1 = new SalesOrderHeader();
    // Add SalesOrderHeader to the Contact.
    contact.SalesOrderHeaders.Add(newSalesOrder1);

    // Create another SalesOrderHeader.
    SalesOrderHeader newSalesOrder2 = new SalesOrderHeader();
    // Add SalesOrderHeader to the Contact.
    contact.SalesOrderHeaders.Add(newSalesOrder2);

    // Get all related ends
    IEnumerable<IRelatedEnd> relEnds =
        ((IEntityWithRelationships)contact)
        .RelationshipManager.GetAllRelatedEnds();

    foreach (IRelatedEnd relEnd in relEnds)
    {
        // Get Entity Collection from related end
        EntityCollection<SalesOrderHeader> entityCollection =
            (EntityCollection<SalesOrderHeader>)relEnd;

        Console.WriteLine("EntityCollection count: {0}",
            entityCollection.Count);
        // Remove the first entity object.
        entityCollection.Remove(newSalesOrder1);

        bool contains = entityCollection.Contains(newSalesOrder1);

        // Write the number of items after one entity has been removed
        Console.WriteLine("EntityCollection count after one entity has been removed: {0}",
            entityCollection.Count);

        if (contains == false)
            Console.WriteLine("The removed entity is not in in the collection any more.");

        //Use IRelatedEnd to add the entity back.
        relEnd.Add(newSalesOrder1);
        Console.WriteLine("EntityCollection count after an entity has been added again: {0}",
            entityCollection.Count);
    }
}

Remarks

The Remove method also deletes the relationship between the source object and the object being removed from the collection. If the relationship has a referential integrity constraint, calling the Remove method on a dependent object marks both the relationship and the dependent object for deletion. This occurs because the constraint indicates that the dependent object cannot exist without a relationship to the parent. For more information, see ReferentialConstraint Element (CSDL).

Remove returns false when the specified object is not in the collection.

Applies to